In a mobile home the other day I saw a tandem breaker (20A/30A)where the 20A outside Breakers that are connected by a handle tie were feeding 2 separate 120V circuits(not multiwire).I removed the handle tie so that if 1 circuit trips the other won't. Did I do the right thing? These breakers are designed for 2 separate 240V loads.

TG: I think that perhaps 110.3(B) has been violated, but I would never dream of red-tagging it. It is my understanding that breakers are required to be "atoumatic trip", meaning that they will open the circuit regardless of the handles position. With that in mind, I see no problem removing handle ties.